Load weighing system for lift trucks and the like



INVENTOR.

TfiF/VEYS.

June. 30, 1953 w, WISE LOAD WEIGHING SYSTEM FOR LIFT TRUCKS AND THE LIKE Filed Feb. 21 1951 14 427241 Ml l's Patented June 30, 1953 UNITED STATES PATENT OFFICE LOAD WEIGHING SYSTEM FOR LIFT TRUCKS AND THE LIKE William M. Wise, Detroit, Mich.

Application February 21, 1951, Serial No. 212,124

1 Claim.

This invention relates to hydraulic weighing scales and more particularly to a hydraulic weighing system for installation upon a fork lift truck or the like to enable a load to be weighed at the same time as it is lifted by the truck fork.

The advantages of hydraulic scales are well recognized; namely their high accuracy and sensitivity. Also, in my co-pending applications, Serial Numbers 25,006, filed May 4, 1948, and 139,446, filed February 19, 1950, I have disclosed hydraulic scales of compact and rugged construction and of high accuracy and sensitivity, capable of being incorporated in cranes or hoists to weigh loads as they are lifted.

An important object of the present invention is to extend the usefulness of hydraulic scales, and in particular, the scales as disclosed in my said co-pending applications, by rendering it possible for such scales to be employed in association with the lift fork and boom structure of a conventional lift truck to enable the loads handled by the truck to be weighed at the same time as they are lifted by the boom and fork structure.

Some such lift trucks are provided with hydraulic means for raisin the lifting fork, and it has heretofore been proposed that a hydraulic scale or indicator be inserted in the hydraulic lifting system, calibrated in pounds for other units of weight. This proposal was based upon the concept that the hydrostatic pressure in the hydraulic lifting system of such a truck is proportional to the load upon the fork. This concept is roughly true, but due to the inherent character of such trucks, it is necessary that the load always be supported in a position which is far off center with respect to the lifting mechanism. Due to the inherent requirement that the load be located off center, a frictional component is introduced which is so high that the pressure in the hydraulic lifting system does not vary accurately with load variations. Attempts to incorporate hydraulic weighing means in the hydraulic lift mechanisms of such trucks have accordingly failed.

It, therefore, becomes an important object of this invention to provide a fork lift truck having a hydraulic scale which is capable of being actuated in accordance with the weight of a load supported by the lift fork but which scale is not subjected to the deleterious effect of the friction involved in the mounting of the lift fork on the truck boom.

It is also an object of the invention to provide a hydraulic load weighing system for installation on a fork lift truck to weigh the loads handled by the truck with a high degree of accuracy and sensitivity.

Other objects and advantages of the invention will become apparent upon consideration of the present disclosure in its entirety and with reference to the accompanying drawings in which:

Figure 1 is a side elevational view illustrating a forklift truck equipped with a hydraulic weighing system in accordance with the invention, the upper portion of the boom being shown broken away for convenience of illustration;

Fig. 2 is an enlarged vertical sectional view on the line 22 of Fig. 1 showing the pressure gage and indicator dial assembly, and

Fig. 3 is an enlarged longitudinal sectional view on the line 33 of Fig. 1 showing the hydraulic pressure cell employed in this embodiment of the invention.

Referring to the drawings, reference character [0 designates, generally, a fork lift truck having a vertical boom [2 pivotally mounted at its lower end upon the truck structure for swinging movement about a transverse axis in conventional manner and carrying a fork structure, indicated generally at M.

Ihe fork structure is of conventional L-shape form, as shown, and disposed with the horizontal arm or arms 1 B capable of being entered beneath a load to be lifted and transported by the truck, the vertical arm I8 being connected with the boom for movement therewith as well as for vertical movement therealong. Such movement can be arranged to be effected in any known manner, as employed on conventional lift trucks. The means employed for this purpose forms no part of this invention.

According to the invention, the vertical arm [8 of the lift fork is pivotally mounted near its upper end upon a transverse horizontal axis upon a pin 20 carried by a bracket 22 forming part of a slide structure, indicated generally at 23 mounted upon the boom for sliding movement therealong, the slide structure being actuatable in any conventional or suitable manner by the lift mechanism of the truck.

A hydraulic cell, indicated generally at 24 is also carried by and bodily movable with the slide 23. The hydraulic cell 24 (one or more of which may be employed in lateral alignment, as desired) forms part of my hydraulic weighing system and is mounted upon the boom l2 in position so that the lower .portion of the lift fork, suspended from the boom by the upper pivot 20, is held-up against the projecting domed nose 26 of a piston 28, sliddimensions. By way of example, a standardized bin or stock box is shown in outline at'32, such as is employed in factories, workshops and the like to receive loose articles.

Referring again to the hydraulic cell24, this is shown in detail in Fig. 3. The piston 28 is held locked in the cylinder 30, at its nose end, by, a

split retaining ring 34 sprung into an annular groove 36 in the interior of the cylinder. At its opposite end the piston is sealed: within the cylinder, with respect to the fluid pressure'chamber 38, by a resilient toroidal gasket or so-called O'-ring 40 contained in an annular recess 42 in thepiston surface. annular recess 44, between the recess-ill and the pressure chamber 38, in which recess M an annular series of anti-friction balls 45 are accom-- modated', and another annular recess dtadjacent the inside of the lock ring 3 1, in which recess 52 another annular series of anti-friction balls 53 are accommodated. The two series of balls have a certain degree ofaxial play within their re-- spective annular piston recesses, substantially as and for the purpose described in my said copending application Serial Number 139,446. At tached to the end of the cylinder t l by means of a retaining ring 54 is a rubber-like sealing element 52. bridging the space between and tightly connecting the cylinder and piston. At its opposite end, the cylinder is shown fitted with a disc plate 58, secured to the cylinder end, as by screwstud means 60, and having an axial conduit GI openinginto the pressure chamber 38 and communicating with a radial conduit. 62. This con duit 62. is formed at its outer end to receive, as by a screw threadedunion G4, a flexible high pres sure hydraulic hose E56. This hose is guidingly supported upon'the boom i2 and the truck body structure, as'by the clipsfia and extends, in tor" tuous manner, as seen in Fig. l, to a conduit "H which communicatesvariations of pressure in the pressure chamber 38 to the interior of the Bourdon tube "of a Bourdon pressure .gage assembly. This assembly, which forinsrno part of my present invention, is of the same generalconstructionand operation as is disclosed in my said co-pending application No. 139, il6, sorequires no detail description herein. It is sufficient to state that the mechanism involved includes a dial. M and pointer 16 fast on a shaft 18, which shaft, and hence the pointer, is rotated from the Bourdon tube in accordance with the variances of pres sure communicated to the interior of the Bourdon tube through the conduit 10.

The ressure gage and dial assembly is capable of being mounted as a unit upon the lift truck body, as by screw studs 86', in position, as shown in Figure 1, where the dial is readily visible. A shut-offcock, indicated generally at B2, is shown included in the flexible hose line 32, and is capable of manual operation to render the pressure gage and dial assembly inoperative when the same is not required for use.

When weighing a load on the fork l4 it is neces- The'latter. also has another sary that the boom l2 should be vertical. This is insured by the operator arranging that the boom is positioned against a stay or indicating device projecting from the front of the truck and indicated at 84. This may be a flexible blade so that the boom may be moved past the vertical position which it denominates, that is counterclockwise from the osition shownin Fig. 1.

In the use of the inventiomandzwiththe cook 82 open and the boom 1'2 held in a vertical position, if, as shown at 32, a standard or predetermined size stock box, crate or other load which has its weight distributed substantially uniformly thereover in a horizontal direction, is supported upon the fork arm [6 with the left hand end of such load, as seen in Figure 1, situated against thelower end of the vertical fork arm [8, pressure resulting from the applied load will be resolved into a pressure exerted axially against the piston 28 to effect a corresponding movement of the scale pointer 16,- whereby the loadlifted by the fork I4 is weighed and indicated on the dial 14.

The use ofstandard'size stock boxes, bins, carts and the like to hold-loose and unsymmetrical partsis quite conventional practice, as well asthe use of standard sized packages of sheet material, and other uniform packages, liquid containers and the like; In the use of all such standardized loads' with the present invention, the dial 14 would be zeroizedto take into accountthe weight of the box, receptacle, pallet or other tare factor, by rotating the dial-T4 by meansofthe-tare'sebting knob, as more particularlybrought out'in my last mentioned copending application. It follows, therefore, that the dial can be calib'rated to accurately designate the'net load.

Insome cases it might b'e-desired to weigh loads of different physical proportions upon" the same lift truck, as for example, bins or boxes shorter than those of the size indicated at 32; In such event-a stop block 86 is providedf shown as rigidly secured to the horizontal fork arm I6, in a position in which the desired centre of gravity relationship will lie-present if the boxd's so positioned upon the fork arm'l5--that its lefthand end, as seen in Fig. 1; is in contactwith this block 86'. It will be apparent'that such ag block could belongitudinally adjustable along the horizontal fork arm' [6, as by'meansof a screw shaft, and that its proper positioning" for different-sizesof boxes or loads could lie-calibrated uponthefork arm.

The hydraulic weighing system of this invention can also be employed to weigh I a load" slung from beneath the fork arm lfi -an'das indicated at 88in Fig. l. Topermlt this to'bedone, the fork arm I5 is fittedwith a sling block 90,- located at a position correspondingtotherequiredposi tion of the centre of gravityand adapted to receive the sling cords 92 incentra'l-and balanced relation'with respect to the underslung' load 88%;

While it will be apparent that theembodiment or the invention herein disclosed will fulfill-the objects abovestated, it will be appreciated that the invention is susceptibleto modification, variation andchange Withoutdeparting from the proper scopeand fair 'meaning of the subjoined claim. I v

I claim:

In a loadweighing system forclliititrucks-and the like having a vertical boom, a carriageivertigcallyslidably carrled by said boom andsaload supporting fork structure pivoted Tonanddepending from said carriage, hydraulic--pressure-means References Cited in the file of this patent UNITED STATES PATENTS Number Number Name Date Schafer Sept. 20, 1932 Ulinski Dec. 5, 1944 Flynn et a1 July 20, 1948 FOREIGN PATENTS Country Date Germany Dec. 6, 1907 

